EP4360184A1

EP4360184A1 - Method for operating an energy supply system, device for exchanging electrical power in an energy supply system, and energy supply system

Info

Publication number: EP4360184A1
Application number: EP22737784.3A
Authority: EP
Inventors: Marcel Kratochvil; Alexander UNRU
Original assignee: SMA Solar Technology AG
Current assignee: SMA Solar Technology AG
Priority date: 2021-06-24
Filing date: 2022-06-20
Publication date: 2024-05-01
Also published as: DE102021116418A1; WO2022268689A1

Abstract

The invention relates to a method for operating an energy supply system (10), wherein a first and a second DC unit (22, 26, 28) exchange power with an AC bus (20) by means of a first and a second power converter (12, 14, 16, 18), respectively. With transmission by means of a transformer (32), this power is then combined and is converted, by means of a third power converter (34), into a DC grid power of a DC grid (30) and/or vice versa. At least the first DC unit (22) is in the form of an energy generation unit, more particularly a PV system having at least one PV generator (24). A frequency and an amplitude of the AC voltage and/or of the AC current on the AC bus (20) are set. The third power converter (34) sets the frequency on the AC bus (20) in accordance with the DC grid power and, to set the AC voltage and/or the AC current, sets the DC grid power in accordance with the AC bus power. The invention also relates to a device for exchanging electrical power in an energy supply system (10) and to a corresponding energy supply system (10).

Description

Method for operating an energy supply system, device for exchanging electrical power in an energy supply system and

power supply system

technical field

The application relates to the exchange of electrical power in an energy supply system with a DC network, via which electrical power is exchanged with DC consumers and which is at least partially supplied with electrical power from a DC source.

State of the art

Electrical DC networks, referred to below as DC networks, are increasingly being used to supply systems with a large number of consumers, for example so-called industrial DC networks. DC networks can be fed from an electrical AC voltage network, hereinafter referred to as AC network, e.g. from a higher-level energy supply network. As DC network participants, various DC consumers and DC sources can be connected to the DC network via suitable DC branches. DC consumers and DC sources are direct voltage units that consume (DC consumers) or emit (DC sources) electrical direct voltage. Examples of DC sources are DC energy generation units, e.g. PV systems, or batteries, which can also be operated either as DC sources or as DC consumers. Depending on which network node is to be connected to a DC branch, a DC branch can be secured via two-pole, fast fluxgate switches for line protection in the event of a short circuit or ground fault. In addition or as an alternative, DC fuses can also be provided.

In a DC network, it may be necessary for safety reasons to couple specific DC units, ie specific DC sources such as power generation units and/or specific DC consumers, to the DC network in a galvanically isolated manner. In the case of a large number of DC Units require considerable effort, for example by providing a galvanic isolation in each corresponding DC branch.

Photovoltaic systems (PV systems) as energy-generating DC sources or storage, such. B. Batteries, as DC units absorbing and releasing energy, can in principle also be connected to the DC grid via non-isolating DC/DC converters, whereby a suitable DC/DC converter should have leakage current detection for safety reasons and, if necessary, determine the insulation resistance of the connected PV system.

In order to avoid from the outset that the overall insulation resistance of the DC grid to the earth potential is influenced by the PV system and/or by the storage or its lines, the PV generators or storage can also have isolating DC/DC converters connected to the DC grid, with the isolating DC/DC converters providing galvanic isolation between the DC grid and the DC unit. Each connected PV generator then requires its own regular insulation monitoring.

In addition, the galvanic isolation of a DC unit from the DC grid may be necessary for other reasons, e.g. if the maximum possible voltage of a connected PV generator against earth potential exceeds the permissible phase-to-earth voltage of the DC grid. Even if the PV system would generate an impermissible asymmetry of the DC system to the ground potential with galvanic coupling to the DC system and/or if a leakage current limit of the DC system would be exceeded regularly or sporadically due to a galvanically coupled PV system.

In general, the length of the DC lines and thus the distance between the DC units and the DC grid is limited for technical reasons. However, a PV system as a DC unit that is designed as a free field or roof system can be located far away from a possible connection point to the DC grid, so that the PV system can be connected over long distances with suitable DC/ PV cables would have to be connected. The same can apply to memories, especially if they have a large capacity and, for example, for security reasons. reasons must be set up away from the DC network of a production facility or similar. Such a connection of a DC unit by means of DC lines can therefore be expensive and inefficient, particularly in the case of DC units that have large and extensive PV generators and/or high-performance storage.

task

The application is based on the object of further improving the supply of a DC network with electrical power from a DC source, and in particular of coupling PV systems or storage devices to a DC network without the DC network beinghave in relation to ground influence.

solution

The object is solved by a method having the features of independent patent claim 1 . The object is solved by a device having the features of independent claim 7 . Advantageous embodiments of the method are claimed in the dependent claims.

Description of the invention

A method for operating an energy supply system with at least one energy generation unit has the following steps:

Exchanging electrical power between a first DC unit and an AC bus via a first power converter, wherein a first DC power of the first DC unit is converted into a first AC power via the first power converter and/or vice versa,

exchanging electrical power between a second DC unit and the AC bus via a second power converter, wherein a second DC power of the second DC unit is converted into a second AC power via the second power converter and/or vice versa,

Merging the first and the second AC power into an AC bus power of the AC bus,

Transferring AC bus power through a transformer, Exchanging electrical power between the AC bus and a DC grid via a third power converter, wherein the AC bus power transmitted by the transformer is converted to DC grid power via the third power converter and/or vice versa.

The first, the second and in particular the third power converter can be designed as bidirectional AC/DC converters which transfer electrical power from their AC side to their DC side and/or vice versa.

At least the first DC unit is designed as an energy generation unit, in particular as a PV system with at least one PV generator. A frequency and an amplitude of the AC voltage and/or the AC current on the AC bus is adjusted by the method. In particular, the third power converter can stabilize the amplitude of the AC voltage by adjusting the DC grid power depending on the AC bus power. The frequency on the AC bus can be adjusted by the third power converter in order to achieve a power balance between the DC power fed into the AC bus as AC power from the DC units and that from the AC unit via the third power converter. to produce the DC mains power dissipated by the bus. In particular, the third power converter can use the set frequency on the AC bus to set the DC power of the DC units fed into the AC bus and thus the AC bus power according to the DC mains power. In addition, the third power converter can intentionally change the DC line power, creating a power imbalance on the AC bus, and modify the frequency on the AC bus. The DC units can adjust their respective DC power depending on the frequency in the AC bus. Feedback between the frequency on the AC bus and the resulting DC network power can thus result in a control circuit that operates largely automatically and has the advantage of being simple to implement in terms of control technology, for example by means of corresponding P(f) characteristics that, in particular, show the dependency of the DC power of the DC units depends on the frequency in the AC bus.

Alternatively or additionally, f(P) control can be used in the third power converter. The third power converter reacts to any Power imbalance with a change in frequency, which in turn can cause a change in the DC power of individual DC units. For example, a change in the irradiation on the PV generator can be compensated for by increasing the power of another DC unit, which includes a storage device, for example, before the DC grid power has to be changed. This allows power balance to be restored and the frequency on the AC bus to be set to a setpoint.

In one embodiment, the first power converter operates the first DC unit in a maximum power operating point and converts the first DC power into a first AC current. The first power converter injects the first AC current onto the AC bus, where the first AC current tracks the AC voltage on the AC bus. For the operation of a PV system in particular, it makes sense to operate the PV generator or generators at the operating point of maximum power, also known as MPP, in order to maximize the yield. A so-called MPP tracker, which can be installed in the first power converter, can take on the task of finding this operating point of maximum power and operating the PV generators at this point.

In one embodiment, the second DC power is generated, stored, and/or consumed by the second DC unit. The second DC power is converted into a second AC current by the second power converter and fed into the AC bus, the second AC current following the AC voltage in the AC bus. The second DC unit can e.g. B. another DC power generation unit, z. B. another PV system, a DC consumer, such. B. electrolyser, or a DC storage, z. B. be a battery. The second power converter can be set up to operate the second DC unit at an adjustable operating point, for example at the operating point of maximum power of a PV generator or at an operating point of maximum efficiency of an electrolyzer; in the case of a storage as the second DC unit, the power exchange with the storage can be adjusted by the second power converter.

In one embodiment, the DC grid power is generated, stored and/or consumed by DC grid subscribers connected to the DC grid. The DC Grid power that is fed into the DC grid by the third power converter can deviate from the total power of the DC grid participants. Any power imbalances in the DC grid can be compensated for by connecting the DC grid to an AC grid, for example to a higher-level energy supply grid, with which electrical power can be exchanged via a suitable grid exchange converter. This mains exchange converter can be responsible for the stable operation of the DC network and have the appropriate measurement, control and regulation technology as well as sufficient power reserves to keep the DC network stable if required using only electrical power from the AC network operate.

The safe operation of the DC grid and in particular the DC grid participants is not impaired by the connection to the remote DC units. In particular, the galvanic isolation of the remote DC units decouples the potentials of the DC network from any isolation and/or leakage current effects that may occur at the remote DC units. Overall, the present invention thus enables simple, cost-effective integration of storage and local energy generation units into the energy supply via a DC network and has proven to be particularly advantageous for use in industrial DC networks that supply a factory with electricity from renewable energy sources, for example can.

In one embodiment, the method comprises exchanging power between the AC bus and another DC unit via another power converter, wherein further DC power of the further DC unit is converted into further AC power via the further power converter will and/or vice versa. In this case, the further DC power can be generated, stored and/or consumed by the further DC unit. The additional DC unit can in particular include an additional DC power generation unit, eg an additional PV system, a DC consumer, such as an electrolyzer, or a DC storage unit, eg a battery. The additional power converter can be set up to operate the additional DC unit at an adjustable operating point. The method offers the advantage that the frequency and/or amplitude of the AC voltage and/or the AC current of the AC bus can be selected relatively freely without being subject to the sometimes strict requirements of a public AC grid. Nonetheless, standard components such as contactors, fuses, monitoring, transformers, etc. can be used, which are also suitable for the conventional public AC mains network. For example, it is possible to use a conventional transformer to electrically isolate the AC bus from the DC grid. It is also possible to ground the transformer used on the AC bus side. In addition, a particularly low-loss operation of the power converter is possible by adjusting the amplitude of the AC voltage on the AC bus, optionally on both sides of the transformer, in the optimal ratio to the amplitude of the DC voltage in the DC grid and optionally on the DC units is set. In addition, the adjustable parameters of the AC bus, ie in particular frequency, voltage and/or idle power, can be used to control and regulate the electrical power transmission in the energy supply system. The power supply system can be operated stably and with reliably predictable power, in particular through a combination of suitable characteristic curves that define dependencies between the frequency on the AC bus and the exchanged power of the power converters involved.

A device for exchanging electrical power in a power supply system with at least one power generation unit has an AC bus to which a first power converter and a second power converter are connected, the first power converter being designed to produce a first DC power of a first DC To convert unit into first AC power and / or vice versa, and wherein the second power converter is designed to convert a second DC power of a second DC unit into second AC power and / or vice versa. The first and second power converters are connected to an AC bus on the AC side, so that the first and second AC power can be transmitted as AC bus power via the AC bus. The device includes a transformer arranged between the AC bus and an AC side of a third power converter, the transformer being configured to transfer the AC bus power and to provide galvanic isolation. The third power converter is for converting the over the Transformer-transmitted AC bus power set up in DC grid power and/or vice versa. A DC network can be connected to a DC side of the third power converter, in which DC network participants can be operated with the DC network power. At least the first DC unit is designed as an energy generation unit, in particular as a PV system with at least one PV generator. The third power converter is configured to adjust a frequency and an amplitude of the AC voltage on the AC bus. In particular, a control unit of the third power converter can adjust the frequency on the AC bus as a function of the DC mains power and the DC mains power as a function of the AC bus power.

The device thus makes it possible to couple several DC units, in particular power generation units, storage devices and consumers, via respective power converters, e.g. DC/AC converters, on the AC side to form an AC bus and to use the electrical power collected in the AC bus to exchange the DC units with the DC grid. The AC bus is galvanically isolated via the transformer and connected to the DC grid via the third power converter.

The frequency and/or the amplitude of the AC voltage and/or the AC current can be optimally designed on the AC bus. Optimum can be based on the design of the overall system and in particular also depend on current conditions, e.g. the solar radiation on a PV system and the DC power currently available as a result. It is also conceivable to make the frequency and/or the amplitude in the AC bus variably adjustable, at least within limits, and to operate the power converters as a function of the current frequency and/or amplitude in the AC bus, in particular by means of f(P) and/or P(f) characteristics.

Thus, the DC grid, where the DC voltage can be essentially fixed, is connected to the AC bus via the third power converter and the transformer. Several DC sources and/or DC consumers are connected to the AC bus, which can be operated with an optimal frequency and/or amplitude of the AC voltage and/or the AC current—possibly also within limits variable respective power converters connected in parallel and set their Power is available to the DC grid via the AC bus, with other repercussions on the safe operation of the DC grid being largely avoided.

In one embodiment of the device, the first power converter is designed to operate the first DC unit in an operating point of maximum power and to convert the first DC power into a first AC current and feed it into the AC bus, the first AC -Current follows the AC voltage in the AC bus.

In one embodiment of the device, a further DC unit can be connected to the AC bus via a further power converter, the further power converter being designed to convert further DC power from the further DC unit into further AC power and /or the other way around. The second and/or the additional DC unit can be set up to generate, store and/or consume the respective DC power.

Optionally, the second DC unit can be designed as a further energy generation unit, in particular as a further PV system with at least one further PV generator. Optionally, the second power converter can then be designed to operate the second DC unit in an operating point of maximum power and to convert the second DC power into a second AC current and to feed it into the AC bus, the second AC current being the AC -Voltage in the AC bus follows.

In one embodiment of the device, the transformer is grounded on its side connected to the AC bus.

In one embodiment of the device, the control is implemented at least partially by the first, the second and/or the third power converter. The first, the second and/or the third power converter can in particular be implemented as a so-called active power converter. In this case, active power converters have a bridge circuit in which power semiconductor switches are actively controlled by a controller for electrical power conversion. The control of the power semiconductor switches and the control of the device can be implemented on the same hardware. Alternatively or additionally, the device can be controlled at least partially outside of the device. In such a case, a controller implemented outside of the device preferably communicates with the device or the individual power converters via a communication interface.

An energy supply system can have such a device as described above. The energy supply system can also have a first DC unit, which is preferably designed as a PV system with at least one PV generator. A second DC unit of the device can also be designed as a PV generator or as an energy store. DC network subscribers can be connected to a DC network of the device in order to draw DC network power. A higher-level AC supply grid can be connected to the DC grid via a grid exchange converter to supply the DC grid.

In one embodiment, the energy supply system has the controller configured to receive a target value for the DC grid power and to operate the first power converter, the second power converter and/or the third power converter such that the DC grid power corresponds to the target value. A suitable target value can include an absolute value, for example a power currently required to supply the DC network, or have a generic value, for example the maximum available regeneratively generated power retrieved from the AC bus.

It is possible to let the DC units and the respective power converters, via which the DC units are connected to the AC bus, interact by means of the controller in such a way that the AC bus as a whole performs special functions for the DC grid can offer. For example, a so-called DC control power can be made available to the DC grid via the third power converter, which serves to stabilize the voltage in the DC grid and between the DC units and the DC grid via the respective power converters and the AC bus is exchanged.

The device thus makes it possible to provide an AC bus for the connection of a PV system, which can be operated separately from a public AC supply network and can therefore be designed in such a way that, on the one hand, AC Standard components such as fuses, converters, transformers, residual current detection, switch disconnectors, AC cables, etc. can be used and, on the other hand, some requirements for common public AC supply networks do not necessarily have to be implemented, e.g. the normative specification of a target voltage or target frequency , but can be implemented if necessary. This can be used to achieve a structure that is as simple and efficient as possible, whereby in particular losses along long DC lines and/or due to inefficient galvanically isolating DC/DC conversion and any disruptive influences of potential shifts or leakage currents on the part of the power generation units are avoided can.

The device can save costs and minimize losses, particularly in applications in which several DC units, in particular DC sources, are to be electrically isolated and possibly connected to a DC network over greater distances, for example several hundred meters.

The transformer for galvanic isolation can be arranged as close as possible to the third power converter, e.g. to have as much of the cabling as possible galvanically isolated from the DC network.

characters

The invention is explained in more detail below with the aid of figures.

1 shows an example of an energy supply system,

2 shows an example of a method for operating an energy supply system;

Fig. 3 shows schematically an embodiment of an energy supply system and

4 schematically shows a further embodiment of an energy supply system.

In the figures, identical or similar elements are denoted by the same reference symbols. An exemplary power supply system 10 is shown in FIG. The energy supply system 10 serves in particular to supply DC network subscribers 40 in the DC section 1 with electrical power, which is provided in particular via a network exchange converter 36 from an AC supply network 2 . In this case, the network exchange converter 36 can draw electrical power from the AC supply network 2 and feed it into a DC network 30 to which the DC network participants 40 are connected. For the stable operation of the DC network 30, the network exchange converter 36 can have a suitable controller, which, for example, compensates for power imbalances in the DC network 30 by varying the network exchange power and thereby keeps the DC voltage in the DC network 30 in a permissible range .

The energy generator 3 is arranged outside the DC section 1 and is connected to the DC network 30 via a connection 4 . In order to be able to feed electrical power from the energy generator 3 into the DC network 30 via the connection 3, certain boundary conditions and guidelines must be observed depending on the specific design of the energy generator 3. In particular, a galvanic isolation between the energy generator 3 and the DC network 30 may be necessary for reasons of isolation and safety. Depending on the performance of the energy generator 3, its output can provide part of the electrical power required in the DC network 30 and/or supply the DC network 30 at least at times completely with electrical power; Any additional power from the energy generator 3 can be fed into the AC supply network 2 as excess power via the network exchange converter 36 and/or can be (temporarily) stored within the energy supply system 10 .

A method for operating an energy supply system 10 is shown schematically in FIG. A concrete power supply system 10 with two DC power generation units as DC units, z. B. two PV systems 22, which form the energy generator 3 and whose power is to reach the DC section 1 via the connection 4, is shown as an example in FIG. 2 or FIG. The procedure has the steps: Step S1: Exchanging power between a first PV system 22 and an AC bus 20 via a first power converter 12, with a first DC power of the first PV system 22 being converted into a first AC power via the first power converter 12 and/or vice versa.

Step S2: Exchanging power between a second DC unit 22, 26, 28 and the AC bus 20 via a second power converter 14, 16, 18, whereby a second DC power of the second DC unit 22, 26, 28 via the second power converter 14, 16, 18 is converted into a second AC power and/or vice versa. The second DC unit can be a second PV system 22 for the example in FIG. 2 . For the example of FIG. 3, the second DC unit can e.g. B. the second PV system 22, a battery 26 or a consumer 28 such. B. an electrolyser to be. Additional DC units can e.g. B. the second or a further PV system 22, the battery 26 or a further battery 26 and / or a consumer 28 and / or a further consumer 28 be.

Step S3: Combining the first and the second AC power to form an AC bus power of the AC bus 20.

Step S4: Transmit AC bus power through a transformer 32.

Step S5: Exchanging power between the AC bus 20 and a DC grid 30 via a third power converter 34, wherein the AC bus power transmitted by the transformer 32 is converted into a DC grid power via the third power converter 34 and/or vice versa.

At least the first DC unit 22 is designed as an energy generation unit, in particular as a PV system 22 with at least one PV generator 24 . A frequency and/or an amplitude of the AC voltage and/or the AC current is set on the AC bus 32, with the third power converter 34 setting the DC grid power as a function of the AC bus power. The DC grid power can be specified and the third power converter ensures a balanced power inflow and outflow in the AC bus. The procedure is z. B. performed by a controller that may be part of the power supply system 10.

An embodiment of an energy supply system 10 with two PV systems 22 is shown schematically in FIG. 3 . Each of the PV systems 22 has one or more PV generators 24 . The DC power generated by the PV systems 22 is for each of the PV systems 22 in each case by a power converter 12, 14, as Inverters can be configured, converted into AC power. The AC powers of the power converters 12, 14 are combined on the AC bus 20 as AC bus power. In addition to the two PV systems 22, further DC units can be connected to the AC bus 20 via further power converters. The AC power on the AC bus 20 is transferred to the third power converter 34 via a transformer 32 . The AC power transmitted via the transformer 32 is converted via the third power converter 34, which can be embodied as an active rectifier, into a DC mains power which is exchanged with the DC mains 30 and is thereby available to the DC mains participants 40. The DC network 30 can, for. B. be an industrial DC network that can exchange power via a network exchange converter 36 with a public AC supply network 2 power. For this purpose, the network exchange converter 36 can be connected to the AC supply network 2 on the AC side via a transformer, in particular via a grounded medium-voltage transformer 38 .

Such a design of the energy supply system 10 makes it possible to connect an energy generator 3 with a plurality of DC units 22 to the DC network 30 without having to design the individual power converters 12, 14 with galvanic isolation. The galvanic isolation of the PV systems 22 from the DC grid 30 can, for. B. can be realized via the transformer 32. This allows a more cost-effective realization of a standard-compliant and secure energy supply system 10, since the galvanic isolation of the transformer 32 allows a plurality of DC units 22 to be electrically isolated from the DC network 30 and operated and secured in a coordinated manner.

A further exemplary embodiment of an energy supply system 10 is shown in FIG. 4 . In addition to two PV systems 22, which are connected via a first and a second power converter 12, 14 to an AC bus 20, a storage device 26 for electrical energy is provided, the z. B. is designed as a battery and can store and deliver electrical energy. The memory 26 is connected to the AC bus 20 via the power converter 16 and can take up electrical DC power when charging and deliver it when discharging via the power converter 16 . The power converter 16 is configured to convert the DC power of the storage 26 into AC power and exchange it with the AC bus 20 . In the power supply system 10 is further a DC consumer 28, z. B. an electrolyzer provided. The DC load 28 can be supplied with electrical power from the AC bus 20 via the power converter 28 .

On the AC bus 20 , the electrical power exchanged by the power converters 12 , 14 , 16 , 18 with the AC bus is combined into an AC bus power and transmitted to the third power converter 34 via the transformer 32 . Electrical power is exchanged with the DC network 30 via the third power converter 34, to which DC network subscribers 40 can be connected.

The DC network participants 40 can, for. B. DC consumer or DC generator. Power can also be exchanged between the DC network 40 and the AC supply network 2 via the network exchange converter 36 and, if necessary, the medium-voltage transformer 38 .

The DC units 22, 26, 28 are electrically isolated from the DC network 30 by the transformer 32. The electrical isolation of the transformer 32 is particularly important for a large distance between the DC network 30 and the energy generator 3 and a large number of DC units 22, 26, 28 is sufficient so that the power converters 12, 14, 16, 18 individually assigned to the DC units 22, 26, 28 can be designed without galvanic isolation.

On the AC bus 20, the AC voltage, e.g. B. the amplitude and / or the frequency of the AC voltage can be specified within certain limits and adjusted accordingly. The values for this can be selected largely independently of which values a public grid, for example the AC supply grid 2, would require.

In a possible system design, the DC voltage in the DC network 30 can be specified, e.g. B. through specifications for an industrial DC network. The DC voltage emitted by the PV systems 22 is generally predetermined by the design of the PV generators 24 and is also variable due to the fluctuating irradiation of the sun. The operating voltages of the battery and/or electrolyser can be specified by the design of the units. The disclosed energy supply system 10 offers a number of degrees of freedom for this as a rule different operating voltages, so to couple the voltages in the energy generator 2 and the voltage in the DC network with each other. Examples of parameters that can be optimized in the system design in order to set a desired power flow between energy generator 2 and DC network 1 and AC supply network 3 with as little loss as possible and efficiently are the amplitude and/or the frequency of the AC voltage the AC bus 20 and the transformation ratio of the transformer 32.

A control of an energy supply system 10 according to FIG. 3 or FIG. 4 is described below.

The DC voltage in the DC bus 30 is initially assumed to be given. The third power converter 34 is designed as a power electronic bridge circuit that is operated in a clocked manner, the specific clocking setting a frequency of the AC-side voltage and a transformation ratio of the AC-side voltage relative to the DC-side voltage. The third power converter 34 thus determines the frequency and amplitude of the voltage in the AC bus 20 according to FIG. 3 and FIG , e.g. in a permissible frequency band around a nominal frequency of e.g. 60 Hz or 41.3 Hz.

The voltage of the AC bus 20, thus predetermined in terms of frequency and amplitude, is detected by the power converters 12, 14, 16, 18 on the AC bus 20 and the power converters 12, 14, 16, 18 synchronize their feed with this AC voltage, i.e. they impress an AC current on the essentially given AC voltage in the AC bus 20 .

In the embodiment according to FIG. 3, the third power converter 34 can additionally be regulated in such a way that the PV generators 24 are operated at an operating point of maximum power. For this purpose, the power converters 12, 14 can be operated with a fixed voltage transformation ratio, for example with largely fixed clocking with optimum efficiency. A change in the AC voltage in the AC bus 20 due to the third power converter 34 is thus passed on directly to the PV generators 24 by the power converters 12 , 14 and causes a change in the operating point of the PV generators 24, ie the DC voltage of the PV generators 24 rises and falls with the set AC voltage in the AC bus 20. The third power converter 34 can now depend on the currently converted electrical power sense the AC voltage and increase or decrease the AC voltage to maximize performance. The voltage at which the PV generators 24 deliver their maximum power, taking into account the transformation ratios of the power converters 12, 14, is thus established in the AC bus 20. Should it be necessary or desired to reduce the power fed into the DC grid 30 via the third power converter 34, for example if there is an oversupply of DC power in the DC grid 30, the AC voltage in the AC bus 20 can through the third power converter 34 can be increased or reduced in order to shift the operating point of the PV generators 24 in the direction of open circuit or short circuit and thus reduce the power compared to the operating point with maximum power.

An embodiment of the regulation of the energy supply system 10, which can be applied in particular to the energy supply system 10 according to FIG. 4, can use the energy store 26 on the AC bus 20 efficiently. The amplitude and the frequency of the AC voltage in the AC bus 20 are initially set by the third power converter 34 . For the amplitude and the frequency of the AC voltage in the AC bus 20, all power converters 12, 16, 34 involved are given target values. Each power converter 12, 16, 34 has a specific P(f) or f(P) characteristic (see Fig. 5), which calculates the power P to be converted in each case as a function of the current frequency f in the AC bus 20 or specifies the frequency to be set depending on the current DC network power.

Specifically, characteristic curves P12, P14, P34 for the power converters 12, 14, 34 and, if necessary, characteristic curves P16, P18 for the power converters 16, 18 can be provided. An exemplary embodiment of such characteristic curves is shown in FIG. 5 by way of example. In FIG. 5, the horizontal axis shows the frequency f in the AC bus 20 and the vertical axis shows the power flow P in the energy supply system 10, with positive values denoting a power flow P in the direction of the DC grid 30 and vice versa. In this example, the characteristic curve P34 of the third power converter has a constant gradient and intersects the frequency axis at a frequency f1. The third power converter 34 can output power from the AC bus 20 to the DC network 30 at a frequency above a threshold f1 (rectifier operation) and output power from the DC network 30 to the AC at a frequency below the threshold f1 - Feed bus 20 (inverter operation). A specific specification for a power purchase by the DC network 30 or a withdrawal from the DC network 30 can be made in particular overriding, for example by a maximum utilization of renewable energy is sought and / or by control power based on the stability requirements of the DC Network 30 is provided. In the case of a specific power exchanged via it, the power converter 34 uses the f(P) characteristic to determine the frequency for the AC bus and then sets it.

The power converters 12, 14 of the PV systems 22 can basically adjust the respective operating point of the PV generators 24 to their operating point of maximum power (so-called maximum power point tracking, MPP tracking for short). In the respective characteristic curve P12, P14, this occurs at frequencies below a threshold f2, so that the maximum possible PV power is fed into the AC bus 20 as long as the frequency is below the threshold f2. Above the frequency f2, the power output is reduced and reaches the value zero at a threshold f3.

The power converter 16 of the memory 26 works on the basis of a P(f) characteristic P 16(f), which has a threshold f4 at which the memory 26 exchanges no power. Below the threshold f4, the memory 26 is discharged and above it At threshold f4, memory 26 is loaded.

The frequencies f2, f3, f4 on the characteristic curves P12, P14, P16 are selected here in such a way that the PV systems 22 can always deliver power - either via the AC bus 20 and the third power converter 34 into the DC grid 30 or via the AC bus 20 and the power converter 16 into the memory 26. In particular at the frequency f4, the maximum possible PV power is transmitted to the DC grid 30, with no power being exchanged with the memory 26. Between the thresholds f2 and f3, the DC grid power according to characteristic P34 is lower than the maximum possible PV power, which is nevertheless called up and partly via the third power converter 34 into the DC grid 30 and partly via the power converter 16 into the storage 26 is transferred.

At threshold f1, no power transfer takes place via the third power converter 34, and the PV power flows almost completely into the storage 30. Depending on the capacity of the storage 26 and the current irradiation on the PV systems 22, it may be necessary to transfer the PV -Reduce power compared to MPP power according to characteristic curve P12, P14.

The characteristic curves can be selected in such a way that the memory 26 can also be charged at a time when no PV power is available. In the case of threshold f3 in particular, the third power converter 34 can use the characteristic curve P34 to specify a DC network power which flows from the DC network 30 via the third power converter 34 into the AC bus and from there via the power converter 16 according to the characteristic curve P16 is fed into the memory 26.

A consumer that is optionally additionally arranged in the energy supply system can be connected via a power converter 18 that includes a characteristic curve P18 with threshold f5. Below the threshold f5, the power converter 18 does not draw any power from the AC bus 20, i.e. the power flow according to the characteristic curve P34 is served by the storage device 26 and/or the PV systems 22. Above f5, the electrolyzer 28 is operated with a power according to the characteristic curve P18 and takes a corresponding power from the AC bus 20, which, if necessary, together with the DC power according to the characteristic curve P16 from the memory 26, results in the DC network power according to the characteristic curve P34 .

Due to time-varying influences, the individual characteristic curves P12, P14, P34 and P16 and, if applicable, P18 can change and/or the powers specified as a result cannot be implemented at certain frequencies, for example due to varying irradiation on the PV systems 22 or if the memory is too full or too empty 26. This can be taken into account by the method according to the application, by the third power converter 34 dynamically adjusts the characteristic curve P34 when setting a specific frequency results in a power flow that deviates from the characteristic curve P34. For example, the gradient of the characteristic curve P34 can be greater the higher the instantaneous MPP power of the PV systems 22 is. Alternatively or additionally, the position of the thresholds f1-f5 can be adjusted, for example by the thresholds f1 and f3 coinciding when the memory 26 is not available, for example because it is fully charged.

The frequencies f1, f2, f3, f4, f5 can be matched to one another in such a way that stable and cost-efficient operation with a predictable course of the power exchanged between the AC bus 20 and the DC grid 30 is achieved without a higher-level control of the AC Bus 20 or the power converter connected to it is necessary. It is also possible to integrate further DC units into the AC bus 20, in which case the number of thresholds P(fn) can be correspondingly increased in order to operate the further DC unit efficiently and in a coordinated manner as required. The frequency thresholds f1, f2, f(n) can be selected in such a way that standardized protection technology and other components that are customary in AC networks can be adopted.

The turns ratio of the transformer 32 can be chosen so that all DC units 22, 26, 28 can exchange power with the AC bus 20. It has to be considered that single-level power converters can typically transfer power between a higher DC voltage to a lower AC voltage and vice versa, ie from a lower AC voltage to a higher DC voltage. For galvanic isolation, the transformer 32 can be arranged as close as possible to the third power converter 34 or can be integrated therein, so that any widely branched cabling of the AC bus 20 is routed galvanically isolated from the DC network 30 . Reference character list

10 power supply system

12, 14, 16, 18 power converter 20 AC bus 22 PV system 24 PV generator 26 battery 28 consumer 30 DC grid 32 transformer 34 power converter 36 grid exchange converter 38 medium-voltage transformer 40 DC grid participants PE potential earth

S1, S2, S3, S4, S5 method steps

Claims

patent claims

1. A method for operating an energy supply system (10) with at least one energy generation unit, with the steps:

• exchanging power between a first DC unit (22) and an AC bus (20) via a first power converter (12), wherein a first DC power of the first DC unit (22) via the first power converter (12) is converted into a first AC power and/or vice versa,

• exchanging power between a second DC unit (22, 26, 28) and the AC bus (20) via a second power converter (14, 16, 18), wherein a second DC power of the second DC unit (22 , 26, 28) is converted into a second AC power via the second power converter (14, 16, 18) and/or vice versa,

• Merging the first and the second AC power into an AC bus power of the AC bus (20),

• transferring the AC bus power via a transformer (32),

• Exchanging power between the AC bus (20) and a DC grid (30) via a third power converter (34), whereby the AC bus power transmitted from the transformer (32) is converted into a DC power via the third power converter (34). mains power is converted and/or vice versa,

• wherein at least the first DC unit (22) is designed as an energy generation unit, in particular as a PV system (22) with at least one PV generator (24),

• wherein a frequency and an amplitude of the AC voltage and / or the AC current on the AC bus (20) are set, wherein the third power converter (34) the frequency on the AC bus (20) depending on the Adjusts DC grid power and adjusts DC grid power depending on AC bus power to adjust AC voltage and/or AC current.

2. The method of claim 1, wherein the first power converter (12) the first DC

Unit (22) operates in an operating point of maximum power and the first DC

Converts power into a first AC current and feeds it into the AC bus (20), the first AC current following the AC voltage in the AC bus (20).

3. The method according to claim 1 or 2, wherein the second DC power is generated, stored and/or consumed by the second DC unit (22, 26, 28), the second DC power being supplied by the second power converter (14, 16 , 18) is converted into a second AC current and fed into the AC bus (20), the second AC current following the AC voltage in the AC bus (20).

4. The method according to claim 1 or 2, wherein the DC network power is generated, stored and/or consumed by the DC network participants (40) connected to the DC network (30).

5. The method according to any one of the preceding claims, comprising the step of: exchanging power between the AC bus (20) and a further DC unit (26, 28) via a further power converter (16, 18), wherein a further DC Power of the further DC unit (26, 28) is converted into a further AC power via the further power converter (16, 18) and/or vice versa.

6. The method according to any one of the preceding claims, wherein the further DC power is generated, stored and/or consumed by the further DC unit (26, 28).

7. The method according to any one of the preceding claims, wherein the frequency on the AC bus (20) by the third power converter (34) based on an f (P) - characteristic (P34) is adjusted depending on the DC grid power.

8. The method according to any one of the preceding claims, wherein the DC power of the DC units (22, 26, 28) by the respective power converter (12, 14, 16, 18) based on a P (f) characteristic (P12, P14 , P16, P18) depending on the frequency on the AC bus (20).

9. Device for exchanging electrical power in a power supply system with at least one power generation unit, comprising: an AC bus (20) to which a first power converter (12) and a second power converter (14, 16, 18) are connected, the first

Power converter (12) is designed to convert a first DC power of a first DC unit (22) into first AC power and/or vice versa, and wherein the second power converter (14, 16, 18) is designed to convert a second DC - to convert power from a second DC unit (22, 26, 28) into second AC power and/or vice versa, and wherein the first and second power converters are each connected to an AC bus (20) on the AC side, see above that the first and the second AC power can be transmitted as AC bus power via the AC bus (20), the device having a transformer (32) connected between the AC bus (20) and an AC side of a third Power converter (34) is arranged, the transformer (32) being set up to transmit the AC bus power and to bring about galvanic isolation, the third power converter (34) for converting the transmitted AC bus power into DC mains power and/or is set up vice versa and being on a DC side of the dri tten power converter (34), a DC network (30) can be connected, in which DC network participants (40) can be operated with the DC network power, with at least the first DC unit (22) as an energy generation unit, in particular as a PV system ( 22) is designed with at least one PV generator (24), the third power converter (34) being designed to adjust a frequency and an amplitude of the AC voltage and/or the AC current on the AC bus (20). , wherein in particular a control unit of the third power converter (34) adjusts the frequency on the AC bus (20) as a function of the DC mains power and the DC mains power as a function of the AC bus power.

10. The device according to claim 9, wherein the first power converter (12) is designed to operate the first DC unit (22) in an operating point of maximum power and to convert the first DC power into a first AC current and into the AC Bus (20) to feed, the first AC current follows the AC voltage in the AC bus (20).

11. The device according to claim 9 or 10, wherein a further DC unit (22, 26, 28) can be connected to the AC bus (20) via a further power converter (14, 16, 18), the further power converter (14 , 16, 18) is designed to convert further DC power from the further DC unit (22, 26, 28) into further AC power and/or vice versa.

12. Device according to one of claims 9 to 11, wherein the second and/or the further DC unit (22, 26, 28) are set up to generate, store and/or consume the respective DC power.

13. Apparatus according to any one of claims 9 to 12, wherein the transformer (32) is grounded on its side connected to the AC bus (20).

14. Device according to one of claims 9 to 13, wherein the control is at least partially realized by the first, the second and/or the third power converter (12, 14, 16, 18, 34).

15. Device according to one of claims 9 to 14, wherein the controller is implemented at least partially outside the device.

16. Energy supply system (10) comprising a device according to any one of claims 9 to 15 with:

- a first DC unit (22), which is designed as a PV system (22) with at least one PV generator (24),

- A second DC unit (22, 26), which is designed as a PV system (22) with at least one PV generator (24) or as an energy store (26), and

- A DC network (30) to which DC network subscribers (40) for drawing DC network power and a higher-level AC supply network for supplying the DC network (30) can be connected.

The power system (10) of claim 16, comprising the controller configured to receive a DC grid power setpoint and the first power converter (12), the second power converter (12, 14, 16, 18) and/or to operate the third power converter (34) so that the DC line power corresponds to the setpoint.